Incident Overview
On October 20, 2012, at approximately 11:48 UTC, a serious incident involving a separation minima infringement occurred in the Riga Flight Information Region (FIR) near the point ATRAK. The Transport Accident and Incident Investigation Bureau of the Republic of Latvia (TAIIB) initiated an investigation after receiving notification on October 22, 2012.
Aircraft Involved
- KLM Boeing 737-800, registration PH-BXN, flight KLM903, en route from Amsterdam (EHAM) to Moscow Sheremetyevo (UUEE) with 157 passengers on board.
- Finnair Embraer 190, registration OH-LKH, flight FIN746L, en route from Warsaw (EPWA) to Helsinki (EFHK) with 86 passengers on board.
Flight History
At the time of the incident, the Riga Area Control Centre (ATCC) sector EAST controller was managing nine aircraft. KLM903 established contact on frequency 133.2 MHz at 11:43:19 while cruising at FL380. FIN746L established contact at 11:47:18, cruising at FL390 on route M857.
At 11:47:44, the controller cleared KLM903 to climb to FL390. Shortly after, the controller perceived a conflict with FIN746L at FL390 and instructed KLM903 to disregard the climb and descend back to FL380. The crew of KLM903 acknowledged and reported traffic on TCAS. At 11:48:33, the Short-Term Conflict Alert (STCA) triggered. KLM903 received a TCAS Resolution Advisory (RA) and began descending. FIN746L also received a TCAS RA. The closest proximity recorded was 4.2 NM horizontally and approximately 700 ft vertically, compared to the standard separation minima of 5 NM horizontally and 1,000 ft vertically.
Communications
At 11:47:59, the controller instructed KLM903: "KLM903 disregard last command, descend to FL 380." The pilot responded: "OK, returning now level 380 and we have traffic on TCAS now KLM903." The controller then advised traffic at 2 o'clock, 5 NM. At 11:48:45, the pilot of KLM903 declared a Resolution Advisory, but this transmission was not heard by the controller due to simplex communication limitations.
Radar Data
Radar recordings show that at 11:49:00, KLM903 was at FL382 descending, heading 092 degrees, ground speed 495 knots, while FIN746L was at FL390, heading 012 degrees, ground speed 437 knots. The separation continued to decrease until the aircraft diverged.
Findings
Both aircraft were equipped with TCAS II, which activated during the incident. The TAIIB classified the occurrence as a serious incident and conducted an investigation under Annex 13 and EU Regulation 996/2010.